Mkael Symmonds & Raymond Dolan, University College London
In:- Neuroscience of Preference and Choice – Eds. – Raymond Dolan & Tali Sharot
Keywords: neuroscience of preference/choice, consciousness, orbitofrontal, dopamine P. As far back as the 1960s neuroscience had demonstrated a clear correlation between laboratory rats pressing a lever apparently for pleasure and the electrical stimulation of subcortical dopamine structures. The dopamine system is ancient from an evolutionary point of view. It is shown that fruit flies can make choices that are supported by their dopamine system, without the need for a highly developed prefrontal cortex. Although preferences are seen to be rooted in biology, they also appear flexible and sometimes even inconsistent. However, there is also thought to be a sometimes unconscious default in favour of the status quo. This default requires enhanced neural activity to overcome it, and this is related to activity in the subthalamic nucleus.
The orbitofrontal cortex appears to play an important role in representing the value of sensory inputs, but it does not act in isolation, having reciprocal connections with the parietal, cingulate and insula cortices and with subcortical areas such as the basal ganglia, all of which are involved in evaluation of sensory inputs. A distinction is made between ‘wanting’ and ‘liking’. The latter is taken to refer to immediate sensory pleasure, while ‘wanting’ is related to longer-term anticipated rewards. The authors here suggest that ‘liking’ depends on an endogenous opiod system, while ‘wanting’ is related to the dopamine system. The authors also touch on the existence of ‘exploratory behaviour’ that goes beyond established preferences. This behaviour appears to derive from parts of the prefrontal. The authors think in terms of preferences being based on communication between a network of brain regions rather than any individual region.
A study by Gottfried, O’Doherty & Dolan (2003) showed responses that were not directly related to the stimulus, but where activation decreased, when satiety with a particular sensory input occurred. This study involved activity in the orbitofrontal, the amygdala, the piriform cortex and the midbrain, but only particular sub-regions of the orbitofrontal and the amygdala decreased in response to satiety. Reductions in activity in line with satiety were also observed in the insula cortex and the striatum in the basal ganglia. Recordings in the orbitofrontal have shown a correlation between preferences and the activity of single neurons.
Dopaminergic neurons located in the ventral tegmental and substantia nigra (SN) regions of the mid brain vary their firing in response to reward stimuli, but dopamine release does not always correlate to preference. One suggestion is that these areas monitor the relationship between predicted reward and reward obtained. There are specific dopaminergic projections to brain regions, particularly the striatum and areas of the prefrontal. Modulation of dopamine in the orbitofrontal and the striatum is related to decision taking. The orbitofrontal is particularly involved with the evaluation of stimuli where there has been a learning process, but the anterior cingulate also appears to be involved in the evaluation of actions.
Dopamine depletion in both the ventral striatum area of the basal ganglia and the interior cingulate leads to reduced disposition to making physical efforts. Other neurotransmitters such as noradrenaline and serotonin are thought to be involved in risky decision taking.Tags: choice, dopamine, orbitofrontal, preference Posted by